Add iops to dstat output

The "-r" option adds io request counts.  They are placed next to
the currently present io throughput columns.

Change-Id: I7b4c6f3608afb3714bc997bb4ba005c00eeab61e
diff --git a/stack.sh b/stack.sh
index 23f11fe..a4e6bfd 100755
--- a/stack.sh
+++ b/stack.sh
@@ -884,7 +884,7 @@
 # -------
 
 # A better kind of sysstat, with the top process per time slice
-DSTAT_OPTS="-tcndylp --top-cpu-adv"
+DSTAT_OPTS="-tcndrylp --top-cpu-adv"
 if [[ -n ${SCREEN_LOGDIR} ]]; then
     screen_it dstat "cd $TOP_DIR; dstat $DSTAT_OPTS | tee $SCREEN_LOGDIR/$DSTAT_FILE"
 else